In general, in a Complementary Metal Oxide Semiconductor (CMOS) type solid-state imaging device, a unit pixel is formed with a photo diode which is a light receiving unit and a plurality of transistors, and a plurality of the pixels are arranged two-dimensionally. In the CMOS type solid-state imaging device, respective electrodes of the transistors are connected to a multilayer wiring, and signal charges generated in the photo diode are read as a signal current by desired voltage pulses being applied to the electrodes of the transistors through respective wirings.
In addition, in a Charge Coupled Device (CCD) type solid-state imaging device, the signal charges generated in the photo diode pass through a charge transfer unit (a vertical CCD and a horizontal CCD) configured with CCDs and are supplied to a charge detection unit.
Further, in recent years, a back surface irradiation type imaging device has been put into practical use in which light is applied to a back surface side which is the side opposite to a front surface on which wiring layers are laminated on a device substrate in which the photo diode and the transistors are formed. In the back surface irradiation type imaging device, charges by photoelectric conversion occur most frequently in the back surface side of the device substrate. Therefore, if color mixing occurs due to leakage of electrons generated by photoelectric conversion in a vicinity of the back surface of the device substrate to adjacent pixels, a signal characteristic deteriorates, and thus suppressing the occurrence of such color mixing is important.
However, when the formation of impurities for performing element isolation between the photodiodes is performed by ion implantation from the front surface side of the device substrate and annealing, a method by high-energy implantation disclosed in PTL 1 is employed.
However, in a deep position of the back surface side far from the front surface of the device substrate to which the ion implantation is performed, ions diffuse to extend in a transverse direction. Accordingly, in a fine pixel, since an electric field in the transverse direction in the vicinity of the back surface of the device substrate is weak, it is difficult to suppress the color mixing due to the leakage of electrons generated by the photoelectric conversion to adjacent pixels.
Therefore, as disclosed in PTL 2, the present applicant has proposed a method which physically separates pixels by forming a trench on the back surface of the device substrate and suppresses the leakage of charges to adjacent pixels by embedding metal in the trench portion.